1. Field of Invention
The invention relates to a developing device for forming a thin developer layer on a developer carrying member by use of a layer thickness-regulating member.
2. Description of Related Art
In a conventional developing apparatus that uses a nonmagnetic one-component developer (hereinafter referred to as toner), a thickness-regulating blade made of rubber elastically makes contact with the developing roller to regulate the amount of toner passing between the layer thickness-regulating blade and the developing roller, and thereby a thin toner layer is formed.
For example, Japanese Patent Application Publication No. 60-205472 discloses a technique in which a coefficient of kinetic friction between the layer thickness-regulating blade and the toner is set to be greater than a coefficient of internal friction between toner particles, and the coefficient of kinetic friction between the layer thickness-regulating blade and the toner is set to be greater than that between the developing roller and the toner. By the technique disclosed in this publication, a thin toner layer can be formed on the surface of the developing roller due to a mechanical force, that is, a shearing force.
However, in the technique disclosed in this publication, no consideration is given to the action of an electrostatic force generated when the toner is charged due to friction between toner particles and friction between the toner and the developing roller or the layer thickness-regulating blade. Thus, in the above-mentioned technique where the layer thickness-regulating blade made of rubber elastically makes contact with the developing roller, normally charged toner along with uncharged toner and toner weakly charged to opposite polarity pass between the layer thickness-regulating blade and the developing roller, and are supplied to the surface of a photoconductive drum. When such abnormally charged toner is supplied to the photoconductive drum, it adheres to positions other than where it should adhere, resulting in so-called fogging, which denotes a problem that the toner adheres lightly over the background of an image and reduces image quality.
In view of the foregoing, an object of the invention is to provide a developing device that can form a uniform thin toner layer and eliminate fogging.